Tokiko 'Key' Mima is an android shaped like a pubescent girl who has been growing up, but only when the doctor exchanges her artificial body for an older one. When her creator dies, Key is trapped in the body of a teenage girl who will never age or die, and even though she doesn't really understand how to act human, it is her most treasured dream to become a real girl. Key pins all of her hopes on her creator's last message, which suggests that to become a human girl, she must win the love of 30,000 people. Key leaves her small village for Tokyo to recruit the necessary friends. In the city, she encounters a slimy pornographer and his muscle-bound assistant. She's saved from their clutches by Sakura, a friend from junior high school, which sets a pattern. The alternately bitchy and loving Sakura, the dashing young Tataki, and Tamayo, a self-styled bodyguard from her native village, take turns rescuing Key. Key contains components that the sinister president of Ajo Heavy Industries needs to perfect his unreliable cyborgs. As the president's icy henchman stalks her, Key reveals she possesses superhuman strength, the ability to levitate, and the power to blow up Ajo warrior robots.